//https://leetcode.cn/problems/n-th-tribonacci-number/

class Solution {
public:
    int tribonacci(int n) {
        //1.创建dp表
        //2.初始化
        //3.填表
        //4.返回值

        if (n == 0) return 0;
        if (n == 1 || n == 2) return 1;

        vector<int> dp(n + 1, 0);
        dp[0] = 0, dp[1] = 1, dp[2] = 1;
        for (int i = 3; i <= n; i++)
        {
            dp[i] = dp[i - 1] + dp[i - 2] + dp[i - 3];
        }

        return dp[n];

    }
};

//空间优化--滚动数组
class Solution {
public:
    int tribonacci(int n) {
        //1.创建dp表
        //2.初始化
        //3.填表
        //4.返回值

        if (n == 0) return 0;
        if (n == 1 || n == 2) return 1;

        int a = 0, b = 1, c = 1, d = 0;
        for (int i = 3; i <= n; i++)
        {
            d = a + b + c;
            a = b;
            b = c;
            c = d;
        }

        return d;

    }
};